Poly(1,4-butylene terephthalate) resins are well known and have been widely employed for the production of thermoplastic molded articles. Also, reinforced compositions of poly(1,4-butylene terephthalate) have been commercially available for a number of years. Unfilled poly(1,4-butylene terephthalate) has good processability, strength and toughness. Other key properties include low water absorption resulting in good dimensional stability, low static and dynamic coefficients of friction, good chemical and abrasion resistance, and good electrical properties. However, the unfilled poly(1,4-butylene terephthalate) has relatively low heat deflection temperature which limits its use. Also, unfilled poly(1,4-butylene terephthalate) has a tendency to shrink to a great extent after being molded.
Reinforced poly(1,4-butylene terephthalate) and, particularly, glass reinforced poly(1,4-butylene terephthalate) has additionally increased tensile strength over the unfilled poly(1,4-butylene terephthalate). However, when molded, particularly glass reinforced poly(1,4-butylene terephthalate) has a tendency to become distorted or warped, especially when the molded article has a thin section.